semihosting: fix return value of SYS_READ and SYS_WRITE

semihosting: fix return value of SYS_READ and SYS_WRITE

ARM/RISC-V semihosting calls SYS_READ/SYS_WRITE require
inversion of the result value as described in
"Semihosting for AArch32 and AArch64". Prior to
this patch, this was done correctly only if
(semihosting->is_fileio==false).

This patch has been tested with STM32F446.

Change-Id: I1b34c8d8393f7dfa66ee6539904a2eaf8f9154b0
Signed-off-by: Pavel Kirienko <pavel.kirienko@gmail.com>
Fixes: https://sourceforge.net/p/openocd/tickets/232/
Reviewed-on: https://review.openocd.org/c/openocd/+/6803
Tested-by: jenkins
Reviewed-by: Tim Newsome <tim@sifive.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>